Infectious disease, how bad does it do a body?

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In my post below I respond to Bryan Caplan’s critique of Greg Clark’s claim that disease can increase per capita income because it reduces population (i.e., same population has a bigger resource base to work with).1 I go the route of the two handed economist by suggesting that whether Clark or Caplan is right depends on the details.2 Herrick adds in the comments:

Caplan’s big claim is that almost anything that persistently raises death rates is likely to persistently reduce output per living worker. It that true?

One possible source of persistent increases in death rates that have no impact on productivity: Many kinds of infectious disease.

I’d welcome medically-informed comments on the topic, but it seems possible for infectious disease (from, say the bad sanitation that Clark emphasizes) to raise the chance of dying any given month without appreciably hurting your productivity most of the time.

Scenario: You get sick for a week or two every couple of years, and if you survive, you go back to being productive. If you don’t survive, well then, you’re pushing up the death rate.

As I suggest below I think that Caplan is wrong if he wants to claim that productivity is always decreased in direct proportion to the increased disease load (ergo, death rate) of a population. This would prevent the rise in incomes which Clark predicts as the lower productivity of each individual means that the same amount of land can support fewer people at or above subsistence. In A Farewell to Alms Clark reports a rise in incomes after the Black Death, and, amongst native peoples in the New World after Old World diseases ravaged them. Obviously this is one extreme cause: a highly lethal infectious disease which cuts down a large proportion of the population very quickly, and then recedes. The other scenario is a case where there is an endemic infection which reduces physiological fitness across the whole population, reducing lifespan and increasing death rates, but also dampening economic productivity. Then there are cases where there is a wide variance within the population in regards to susceptibility toward infectious agents. This might be more like the first scenario, a large number of people die very quickly, while many others are spared because of some immunity. And so on.

From Darwinian first principles it seems that there should be a large number of pathogens which are infectious but not fatal. Though reducing physiological fitness, they don’t knock out their host because to do so would result in their own reduced evolutionary fitness. But hey, Herrick asked for expert opinion. I was actually hoping that someone with medical expertise (e.g., tropical diseases?) would weigh in on that thread, but that didn’t happen. So I come to you with open hands and ask you to enlighten….

Update: Greg Clark responds directly to the Caplan critique. As a non-economist I’m more interested in what the empirical historical data says, and what little I know seems to agree with the general thrust of Clark’s point.

1 – That sentence should filter out chimpanzee readers since it should be totally incomprehensible to them.

2 – No shit it depends on the details!



  1. I think that Mr. Caplan has got it right. The burden of a disease is not only the physiological damage to an organism, or the psychological suffering that anyone has already passed by. There are social and economical costs, paid by the sick, their family and the State. One would say that letting the sick die would improve general income. That would be the same as to say that if half of the population of a hypothetical town was killed, let’s say, by cholera, then per capita wealth would double. The issue is, after all sick die, who will produce wealth? The living. They will not double the production of wealth to keep the total amount of wealth stable. Some of the town’s citizens would not be killed by cholera, but would become too weak to work, and would become extra cost for the wealth-producing citizens. This is taken in consideration when planning public health policies. Vaccines, sanitation and antibiotics are indeed expensive, but the costs of not treating is higher. Sorry for the general lack of quotations on papers or other sources, but this is basic medical knowledge.

  2. But Clark is speaking of a time before the modern welfare state, vaccines, sanitation, and all the rest. In fact, he points out the higher quality of life (based on wages as an amount of wheat/calories available per person) in England as opposed to Japan during a period in which the English dumped their offal in the streets and didn’t provide bathrooms for party guests. 
    If every family is touched by death 
    (rich and poor), and there is no welfare state, then Clark is likely right. Most of the death rate is caused by children dying of diseases their parents have already had and presumably become immune to, so it shouldn’t deal them a further physical blow even if half their children succomb in a single day. If some ailment is killing off adults, the survivors don’t have to make up all the production of the dead to see a benefit (i.e. double their output in the last example), they just have to produce slightly (but significantly) more than they did at the higher population level. If the town had been overpopulated (above carrying capacity) beforehand, causing individuals to reduce each others production through space issues, than this should be easy to do. 
    I think people in general were a lot hardier back then, having survived childhood diseases, and were not likely to claim emotional and physical suffering as an excuse not to produce enough (or more) food for their surviving family. What are some aches and nightmares versus death of starvation, or preventing the death of an extra child? 
    To summarize, I thought Clark’s whole point was that humans during the Malthusian era were subject to the same parameters used in ecological models that predict the population size of animals, and to the same selective forces as animals as a result. You don’t have to be the most productive man in the world, you just need to be slightly more productive than other people (and have that translate into offspring). It helps if those other people are removed.

  3. Haven’t read everything, but Geertz’s “Agricultural Involution” and Elvin’s “Pattern of the Chinese Past” both deal with dense near-subsistence populations. According to Geertz, in Indonesia extra hands could always be put to work cultivating the land even more intensively, but obviously there would be diminishing returns. Elvin talks about the “high-level equilibrium trap”, where a dense and productive population gets stuck at the survival level and is not able to advance. 
    In both these cases, thinning the population would move surviving labor to the most productive land and away from the less-productive land, increasing the per-capita productivity. In turn, populations farther from subsistence would have more resources / labor available for investment and might be able to escape the equilibrium. 
    This may have been covered on one of the other threads or in the book itself. If so, sorry.

  4. Technological shifts have short-term consequences for income per person in the Malthusian logic. Shifts in the death schedule has permanent consequences. 
    A a new disease, even one that makes people less productive, may have a short term hit on incomes via the technological shift, but it has a permanent effect on the death schedule. 
    The black death was a “one-time” event. Its a nice case of the perversity of the Malthusian trap, but I don’t think its what Prof. Clark had in mind in the quote Caplan cites at the beginning of his first post on the subject.

  5. I should have mentioned that the short term effect, due to a technology shift, of disease may be negative, but the long-term effect, due to the death schedule shift, is positive. 
    The short term drop in incomes “fixes” itself in the long run (as people die) and all we’re left with is the long-run positive effects of disease. 
    Compare two societies, one with some disease and the other with the same disease and one other. The second society would have a death schedule pushed more to the right and thus higher incomes per person. This is true even if the second societies technology schedule is lower than the first’s.

  6. With cholera, you either die in a short time or recover fully. The same, most of the time, for smallpox, yellow fever, typhus, typhoid, and a host of childhood infections.  
    There are chronic diseases that reduce work output – many involve parasitic worms: ascariasis, schistosomiasis, hookworm, filariasis, dracunculiasis, onchocerciasis, loa loa.  
    Also falciparumj malaria, but it often kills as well.

  7. Re: the update & Clark’s (persuasive) reply, this strikes me as a good example of how theory without knowledge of history can lead one astray. I don’t think Bryan knows anywhere near as much as Clark does about what actually happened, so all he’s got to go on is his models. I think if he did know the historical details he’d have seen right away that his argument contra Clark was historically implausible, and so Clark has the advantage here because he has data in addition to theory. (This is what gives Greg Cochran the intellectual advantage a lot of the time too.)

  8. the update & Clark’s (persuasive) reply, this strikes me as a good example of how theory without knowledge of history can lead one astray.  
    i was thinking the same thing. bryan was wandering in “let us assume” land and then deriving from models based on his assumptions.

  9. I would like to put some of the comments here in perspective. 
    In the past most families were touched by death, indeed, and many children died before 1 year old. However, one cannot prove that the greatest losses were during infancy anbd chilhood. There is evidence for the opposite. Children were more affected by infectious diseases, and they were the first to benefit from reductions of infections. This reduction can be accounted by improvements in nutrition and public health caused by economic growth(1). 
    The idea of reducing the population so wealth can be increased is not new at all. It has been first elaborated in the 18th century by Malthus. It says namely that lolwering the population of poor people by means of restricion would effectively decrease poverty. Other aspect of the idea is called theory of population and had profound influence on Darwin himself and the original idea of species competition. However, Darwin also noted that the thory was applied to animals without human intelligence. This determinism was criticized by (who?) Marx (2). 
    I think people are a little bit biased by social aspects when discussing on biology. 
    My bias is the one of a citizen of a 3rd world country. Here, infectious diseases, chronic illnesses and the losses they cause on economy are not theory. Everyday public health administrators face with the problem of a non-producing, sick population that have to be supported by bthe welfare state. I would be very glad if someone could explain me how to increase wealth of a population just letting the sick go. 

  10. bryan was wandering in “let us assume” land and then deriving from models based on his assumptionsIn any case, he was misunderstanding Clark’s view on the theory too. When Clark says “in equilibrium real incomes would still be higher,” he means that ignoring the dynamics in the transition from equilibrium to equilibrium, when the economy settles down again into its new equilibrium, incomes will be higher. I assume, by endorsing the diagram linked to in the update, Clark would agree that in the transition to the new equilibrium, incomes might be smaller.  
    Clark is doing what economists call comparative statics. This is just answering questions like: All else equal, do societies with more diseases have higher incomes?  
    I’m surprised Caplan got tripped up by that because economists rarely discuss transition dynamics.

  11. In the past most families were touched by death, indeed, and many children died before 1 year old. However, one cannot prove that the greatest losses were during infancy anbd chilhood. There is evidence for the opposite. Children were more affected by infectious diseases, and they were the first to benefit from reductions of infections.  
    i have no idea what you are trying to say here, it sounds contradictory, so i assume that the problem is linguistic presentation. 
    Everyday public health administrators face with the problem of a non-producing, sick population that have to be supported by bthe welfare state.  
    why do you keep talking about public heath administrators? modern situations aren’t analogous to pre-modern ones. even in most third world nations average life expectancy is now greater than 60.

  12. Its pretty well known in developing countries productivity is reduced by the burden of infectious disease. One company in South Africa noted that every time a worker became efficient at their job, they came down with AIDS. Malaria has a similar effect. Some factories in the third world have found a hot meal increases productivity,a small improvement in nutrition suffices.

  13. The idea that disease is good is an extrapolatin of an absurd model used in economics, called the Solow Model. 
    What it implies is that if population growth were lower per lower per a given savings rate the output per worker would be higher since there would be more capital availber per worker. 
    Implying higher productivity. Of course these models fail to take into to account the fact that industrialized countries also have “paygo” social welfare systems and “medical systems” that require taxes from workers to support retirees. 
    Or the fact that retirees need to be supported. 
    So although in theory developing countries with high population growth rates are at a disadvantage versus industrialized country they do have more workers per retiree, also life expectancy is lower so even if you do collect retirement benefits chances are you probably wouldn’t use them as long as someone in an industrialized country. 
    However back to Solow’s model I think its highly flawed for this very reason. Although I don’t think it would be too difficulto add some sort of stochastic to adjust for aging. 
    A population’s average age is related to its fertility or “growth rate”. The higher the growth rate the lower the average age, this would be an easy variable to add back into the model to account for a population “aging”. 
    In effecting aging might be modeled as a variation of frequency dependent selection, although my math skills suck, this definitely looks very similar to that.